JP4696355B2 - Organic EL device - Google Patents

Description

【００５９】
【化２】

【００６０】
【化３】

【００６１】
有機発光層のホスト物質として用いられる電子輸送性化合物としては、キノリン誘導体が好ましく使用することができ、さらには、8−キノリノールないしその誘導体を配位子とする金属錯体、とくに、下式の構造を有するトリス（8−キノリナト）アルミニウム（Alq3）が好ましく使用される。また、フェニルアントラセン誘導体やテトラアリールエテン誘導体も、電子輸送性化合物として使用することができる。
【００６２】
【化４】

【００６３】
本発明において、有機発光層は、正孔輸送性化合物もしくは電子輸送性化合物またはこれらの混合物であるホスト物質に、蛍光物質であるドーバントがドープされた構造を有していることが好ましい。
【００６４】
また、本発明にかかる有機EL素子は、好ましくは、互いに積層された2層の有機発光層を備えている。2層の有機発光層を形成する場合には、それぞれに、異なった発光波長を有する蛍光物質をドーピングすることによって、広い発光波長帯域を確保し、また、発光色の色彩の自由度を向上させることができる。
【００６５】
本発明において、ドーバントとして含有させる蛍光物質としては、たとえば、特開昭63−264692号公報に開示された化合物、具体的には、ルブレン系化合物、クマリン系化合物、キナクリドン系化合物、ジシアノメチルビラン系化合物などの化合物よりなる群から選ばれる1種以上の化合物が好ましく使用できる。
【００６６】
本発明に好ましく使用できる蛍光物質の例を挙げると、以下のとおりである。
【００６７】
【化５】

【００６８】
【化６】

【００６９】
【化７】

【００７０】
【化８】

【００７１】
さらに、本発明においては、特開2000−26334号公報および特開2000−26337号公報に記載されているナフタセン系化合物も、ドーバントとして含有させる蛍光物質として、好ましく使用することができ、ルブレン系化合物、クマリン系化合物、キナクリドン系化合物、ジシアノメチルピラン系化合物などと併用することによって、有機EL素子の寿命を飛澤的に向上させることができる。
【００７２】
本発明において、ドーバントとして含有させる蛍光物質として、好ましく使用することのできるナフタセン系化合物は、式（Ｉ）で示される基本骨格を有している。
【００７３】
【化９】

式（Ｉ）において、Ｒ¹ 〜Ｒ⁴ はそれぞれ非置換、または置換基を有するアルキル基、アリール基、アミノ基、複素環基およびアルケニル基のいずれかを表す。また、好ましくはアリール基、アミノ基、複素環基およびアルケニル基のいずれかである。
【００７４】
Ｒ¹ 〜Ｒ⁴ で表されるアリール基としては、単環もしくは多環のものであってよく、縮合環や環集合も含まれる。総炭素数は、６〜３０のものが好ましく、置換基を有していても良い。
【００７５】
Ｒ¹ 〜Ｒ⁴ で表されるアリール基としては、好ましくはフェニル基、（ｏ−，ｍ−，ｐ−）トリル基、ピレニル基、ペリレニル基、コロネニル基、（１−、および２−）ナフチル基、アントリル基、（ｏ−，ｍ−，ｐ−）ビフェニリル基、ターフェニル基、フェナントリル基等である。
【００７６】
Ｒ¹ 〜Ｒ⁴ で表されるアミノ基としては、アルキルアミノ基、アリールアミノ基、アラルキルアミノ基等いずれでも良い。これらは、総炭素数１〜６の脂肪族、および／または１〜４環の芳香族炭素環を有することが好ましい。具体的には、ジメチルアミノ基、ジエチルアミノ基、ジブチルアミノ基、ジフェニルアミノ基、ジトリルアミノ基、ビスジフェニリルアミノ基、ビスナフチルアミノ基等が挙げられる。
【００７７】
Ｒ¹ 〜Ｒ⁴ で表される複素環基としては、ヘテロ原子としてＯ，Ｎ，Ｓを含有する５員または６員環の芳香族複素環基、および炭素数２〜２０の縮合多環芳香複素環基等が挙げられる。
【００７８】
Ｒ¹ 〜Ｒ⁴ で表されるアルケニル基としては、少なくとも置換基の１つにフェニル基を有する（１−、および２−）フェニルアルケニル基、（１，２−、および２，２−）ジフェニルアルケニル基、（１，２，２−）トリフェニルアルケニル基等が好ましいが、非置換のものであってもよい。
【００７９】
芳香族複素環基および縮合多環芳香複素環基としては、例えばチエニル基、フリル基、ピロリル基、ピリジル基、キノリル基、キノキサリル基等が挙げられる。
【００８０】
Ｒ¹ 〜Ｒ⁴ が置換基を有する場合、これらの置換基のうちの少なくとも２つがアリール基、アミノ基、複素環基、アルケニル基およびアリーロキシ基のいずれかであることが好ましい。アリール基、アミノ基、複素環基およびアルケニル基については上記Ｒ¹ 〜Ｒ⁴ と同様である。
【００８１】
Ｒ¹ 〜Ｒ⁴ の置換基となるアリーロキシ基としては、総炭素数６〜１８のアリール基を有するものが好ましく、具体的には（ｏ−，ｍ−，ｐ−）フェノキシ基等である。
【００８２】
これら置換基の２種以上が縮合環を形成していてもよい。また、さらに置換されていても良く、その場合の好ましい置換基としては上記と同様である。
【００８３】
Ｒ¹ 〜Ｒ⁴ が置換基を有する場合、少なくともその２種以上が上記置換基を有することが好ましい。その置換位置としては特に限定されるものではなく、メタ、パラ、オルト位のいずれでも良い。また、Ｒ¹ とＲ⁴ 、Ｒ² とＲ³ はそれぞれ同じものであることが好ましいが異なっていてもよい。
【００８４】
また、Ｒ¹ 〜Ｒ⁸ のうちの少なくとも５種以上、より好ましくは６種以上が非置換または置換基を有するアルキル基、アリール基、アミノ基、アルケニル基または複素環基である。
【００８５】
Ｒ⁵ ，Ｒ⁶ ，Ｒ⁷ およびＲ⁸ は、それぞれ水素または置換基を有していても良いアルキル基、アリール基、アミノ基およびアルケニル基のいずれかを表す。
【００８６】
Ｒ⁵ ，Ｒ⁶ ，Ｒ⁷ およびＲ⁸ で表されるアルキル基としては、炭素数が１〜６のものが好ましく、直鎖状であっても分岐を有していても良い。アルキル基の好ましい具体例としては、メチル基、エチル基、（ｎ，ｉ）プロピル基、（ｎ，ｉ，ｓｅｃ，ｔｅｒｔ）−ブチル基、（ｎ，ｉ，ｎｅｏ，ｔｅｒｔ）−ペンチル基等が挙げられる。
【００８７】
Ｒ⁵ ，Ｒ⁶ ，Ｒ⁷ およびＲ⁸ で表されるアリール基、アミノ基、アルケニル基としては、上記Ｒ¹ 〜Ｒ⁴ の場合と同様である。また、Ｒ⁵ とＲ⁶ 、Ｒ⁷ とＲ⁸ は、それぞれ同じものであることが好ましいが、異なっていても良い。
【００８８】
本発明において、ドーバントとして含有させる蛍光物質として、好ましく使用することのできる化合物には、たとえば、次のものが挙げられる。
【００８９】
【化１０】

【００９０】
【化１１】

【００９１】
二層の有機発光層を設ける場合、各有機発光層が、２種以上のこれらの蛍光物質を含み、２種以上の蛍光物質が、異なった発光波長を有していることが好ましい。
【００９２】
本発明において、有機発光層におけるドーバントの含有量は、０．０１〜２０重量％であることが好ましく、さらに好ましくは、０．１〜１５重量％である。
【００９３】
本発明において、有機発光層の厚さはとくに限定されるものではなく、その好ましい厚さは、形成方法によっても異なるが、通常、５〜５００nm、さらに好ましくは、１０〜３００nmである。
【００９４】
本発明において、二層以上の有機発光層を形成する場合、各有機発光層の厚さは、分子層一層分に相当する厚さから、有機発光層全体の厚さ未満の範囲にあり、具体的には、１〜８５nm、好ましくは５〜６０nm、さらに好ましくは５〜５０nmである。
【００９５】
本発明において、好ましくは、有機発光層は蒸着によって形成される。
【００９６】
本発明において、有機発光層を、蒸着によって形成する条件は、とくに限定されるものではないが、１×１０^-4パスカル以下で、蒸音速度を０．０１〜１nm／秒程度とすることが好ましい。
【００９７】
本発明において、好ましくは、有機発光層は、正孔輸送性化合物と電子注入輸送性化合物の混合物を含んでいる。
【００９８】
有機発光層が、正孔輸送性化合物と電子注入輸送性化合物の混合物を含んでいる場合には，キャリアのホッピング伝導パスが形成されるため、各キャリアは極性的に優勢な物質中を移動し、逆の極性のキャリア注入が起こり難くなり、したがって、有機発光層に含まれた化合物がダメージを受けることが防止されるので、素子の寿命を向上させることができるという利点がある。
【００９９】
さらに、蛍光物質からなるドーバントを、正孔輸送性化合物および電子注入輸送性化合物の混合物を含んだ有機発光層に含有させることによって、有機発光層自体が有する発光波長特性を変化させることができ、発光波長を長波長側に移行させるとともに、発光強度を向上させ、さらには、有機EL素子の安定性を向上させることが可能になる。
【０１００】
有機発光層が、正孔輸送性化合物および電子注入輸送性化合物の混合物を含んでいる場合、正孔輸送性化合物と電子注入輸送性化合物の混合比は、それぞれのキャリア移動度とキャリア濃度にしたがって決定されるが、一般的には、重量比で、1／99〜99／1、好ましくは、10／90〜90／10、さらに好ましくは、20／80〜80／20、最も好ましくは、40／60〜60／40が選ばれる。
【０１０１】
正孔輸送性化合物および電子注入輸送性化合物の混合物を含む有機発光層を形成する場合には、正孔輸送性化合物と電子注入輸送性化合物を、異なる蒸着源に入れて、蒸発させ、共蒸著することが好ましいが、正孔輸送性化合物と電子注入輸送性化合物の蒸気圧が同程度あるいは非常に近い場合には、あらかじめ同じ蒸着源内で混合させておき、蒸著することもできる。
【０１０２】
正孔輸送性化合物および電子注入輸送性化合物の混合物を含む有機発光層を形成する場合、有機発光層内で、正孔輸送性化合物と電子注入輸送性化合物とが均一に混合していることが好ましいが、均一に混合していることは必ずしも必要でない。
【０１０３】
本発明において、有機物層は、好ましくは、少なくとも一層の有機発光層に加えて、正孔を安定的に輸送する機能を有する正孔輸送層、ならびに、電子を安定的に輸送する機能を有する電子輸送層を備えている。これらの層を備えることによって、有機発光層に注入される正孔や電子を増大させるとともに、有機発光層内に閉じ込めさせ、再結合領域を最適化させ、発光効率を向上させることが可能になる。
【０１０４】
本発明において、正孔輸送層に、好ましく使用することができる化合物としては、例えば、テトラアリールベンジシン化合物（トリアリールジアミンないしトリフェニルジアミン：TPD）、芳香族三級アミン、ヒドラゾン誘導体、カルバゾール誘導体、トリアゾール誘導体」イミダゾール誘導体、アミノ基を有するオキサジアゾール誘導体、ポリチオフェンなどを挙げることができる。これらのうち、テトラアリールべンジシン化合扮（トリアリールジアミンないしトリフェニルジアミン：TPD）、WO／98／30071号に記載されているトリアリールアミン多量体（ATP）が、とくに好ましく使用することができる。
【０１０５】
トリアリールアミン多量体（ATP）の好ましい具体例は、以下のとおりである。
【０１０６】
【化１２】

【０１０７】
【化１３】

【０１０８】
【化１４】

【０１０９】
本発明において、さらには、特開昭63−295695号公報、特開平2−191694号一公報、特開平3−792号一公報、特開平5−234681号公報、特開平5−239455号公報、特開平5−299174号公報、特開平7−126225号公報、特開平7−126226号一公報、特開平8−100172号公報、EPO650955Alなどに記載されている各種有機化合物も、正孔注入輸送層、正孔注入層および正孔輸送層に使用することができる。
【０１１０】
本発明において、２種以上のこれらの化合物を併用してもよく、２種以上のこれらの化合物を併用する場合には、一層中に混合しても、また、２以上の層として、積層してもよい。
【０１１１】
本発明において、正孔輸送層は、前記化合物を蒸着することによって形成することができる。蒸着によって、素子化する場合には、均一で、ピンホールのない１〜１０nm程度の薄膜を形成することができるため、正孔注入層にイオン化ポテンシャルが小さく、可視波長の光を吸収する化合物を用いても、発光色の色調変化や再吸収による発光効率の低下を防止することができる。
【０１１２】
本発明において、電子輸送層に、好ましく使用することができる化合物としては、たとえば、トリス（8−キノリノラト）アルミニウム（Alq3）などの8−キノリノールないしその誘導体を配位子とする有機金属錯体、オキサジアゾール誘導体、ペリレン誘導体、ピリジン誘導俸、ピリミジン誘導体、キノキサリン誘導体などを挙げることができる。
【０１１３】
本発明において、電子輸送層は、前記化合物を蒸着することによって形成することができる。
【０１１４】
本発明において、有機発光層、正孔注入輸送層あるいは正孔注入層および正孔輸送層、ならびに、電子注入輸送層あるいは電子注入層および電子輸送層の各層を、蒸着によって形成する条件はとくに限定されるものではないが、１×１０^-4パスカル以下で、蒸着速度を０．０１〜１nm／秒程度とすることが好ましい。各層は、１×１０^-4パスカル以下の減圧下で、連続して、形成されることが好ましい。１×１０^-4パスカル以下の減圧下で、連続して、各層を形成することによって、各層の界面に不純物が吸着されることを防止することができるから、高特性の有機EL素子を得ることが可能になるとともに、有機EL素子の駆動電圧を低下させ、ダークスポットが発生し、成長することを抑制することができる。
【０１１５】
本発明において、有機発光層、正孔輸送層、電子輸送層に、２種以上の化合物を含有させる場合には、化合物を入れた各ボートを個別に温度制御して、共蒸着によって、有機発光層、正孔輸送層、電子注入輸送層、電子注入層あるいは電子輸送層を形成することが好ましい。
【０１１６】
本発明において、前記電子輸送層に代えて、あるいは、加えて、電子の導通パスを備え、正孔をブロックする機能を有する高抵抗の無機電子注入輸送層を設けることもできる。
【０１１７】
このように、電子の導通パスを備え、正孔をブロックする機能を有する高抵抗の無機電子注入輸送層を、有機発光層と電子注入電極との問に、設けることによって、有機発光層に電子を効率よく注入することができ、発光効率を向上させることが可能となるとともに、駆動電圧を低下させることが可能になる。さらには、電子の導通パスを備え、正孔をブロックする機能を有する高抵抗の無機電子注入輸送層を設けることによって、有機ELディスプレイパネルおよび有機EL素子の厚さを減少させることができ、蒸着によって、カラーフィルター層ないしカラーフィルターを形成することによって薄層化された有機ELディスプレイパネルおよび有機EL素子をより一層薄層化することが可能となる。
【０１１８】
高抵抗の無機電子注入輸送層は、好ましくは第１成分として仕事関数４eV以下、より好ましくは１〜４eVであって、
好ましくはＬｉ，Ｎａ，Ｋ，Ｒｂ，ＣｓおよびＦｒから選択される１種以上のアルカリ金属元素、または、
好ましくはＭｇ，ＣａおよびＳｒから選択される１種以上のアルカリ土類金属元素、または、
好ましくはＬａおよびＣｅから選択される１種以上のランタノイド系元素のいずれかの酸化物を含有する。これらのなかでも、特に酸化リチウム、酸化マグネシウム、酸化カルシウム、酸化セリウムが好ましい。これらを混合して用いる場合の混合比は任意である。また、これらの混合物中には酸化リチウムがＬｉ₂Ｏ換算で、５０ mol％以上含有されていることが好ましい。
【０１１９】
無機電子注入層は、さらに第２成分としてＺｎ，Ｓｎ，Ｖ，Ｒｕ，ＳｍおよびＩｎから選択される１種以上の元素を含有する。この場合の第２成分の含有量は、好ましくは０．２〜４０ mol％、より好ましくは１〜２０ mol％である。この含有量が少ないと電子注入機能が低下し、含有量が多くなると正孔ブロック機能が低下してくる。２種以上を併用する場合、合計の含有量は上記の範囲にすることが好ましい。第２成分は金属元素の状態でも、酸化物の状態であってもよい。
【０１２０】
このように、高抵抗である第１成分中に、第２成分として、Ｚｎ、Ｓｎ、Ｖ、Ｒｕ、ＳｍおよびＩｎよりなる群から選ばれる1種以上の元素を、０．２〜４０ mol％含有させて、導電パスを形成することにより、電子注入電極から有機発光層に、効率よく、電子を注入することができる。これは、第一成分中に、第二成分を含有させることによって、絶縁物質中に、導電物質が島状に存在することになり、電子注入のためのホッピングパスが形成されるためと考えられる。
【０１２１】
第１成分中に、第２成分を、０．２〜４０ mol％含有させることにより、さらに、有機発光層から電子注入電極への正孔の移動を抑制することが可能になり、有機発光層において、正孔と電子とを効率よく再結合させることができ
る。
【０１２２】
高抵抗の無機電子注入輸送層を設ける場合には、従来の有機の電子注入輸送層や、有機の電子注入層、有機の電子輸送層を有する有機EL素子に比して、同等か、それ以上の輝度を得ることができ、しかも、耐熱性、耐侯性が高いので、寿命が長く、無機材料である電子注入電極との接続性も良好になり、そのため、リークやダークスポットの発生も少ないという利点がある。さらには、比較的高価な有機物質とは異なり、無機電子注入輸送層を形成するための無機物質は、安価で、入手がしやすく、無機電子注入輸送層の形成も容易であるので、有機EL素子ないし有機ELディスプレイパネルの製造コストを低減させることができる。
【０１２３】
高抵抗の無機電子注入輸送層の抵抗率は、１×１０^-2Ω・cm〜１×１０^-8Ω・cmであることが好ましい。無機電子注入輸送層の抵抗率をかかる範囲に設定することによって、高い正孔ブロック性を維持しつつ、電子注入効率を飛躍的に向上させることが可能になる。
【０１２４】
第１成分の酸化物は、通常、化学量論組成（stoichiometric composition）であるが、これから、多少偏倚して、非化学量論組成（non−stoichiometry）となっていてもよい。第２成分の酸化物も同様である。
【０１２５】
高抵抗の無機電子注入輸送層は、さらに、不純物として、Hや、スパッタガスとして用いるＮｅ、Ａｒ、Ｋｒ、Ｘｅなどを、合計５at％以下含有していてもよい。
【０１２６】
高低抗の無機電子注入輸送層は、通常、非晶質状態である。
【０１２７】
高抵抗の無機電子注入輸送層は、０．２〜３０nmの膜厚を有していることが好ましく、０．２〜２０の膜厚を有していると、とくに好ましい。高抵抗の無機電子注入輸送層の膜厚が、０．２nm未満でも、３０nmを超えていても、電子注入の機能が十分に発揮されなくなる。
【０１２８】
高抵抗の無機電子注入輸送層は、スパッタリング、蒸着など、各種の物理的あるいは化学的な薄膜形成方法によって、形成することができるが、スパッタリング法によって形成することが好ましい。とくに、第１成分と第２成分を、ターゲットとして、別個にスパックリングする多元スパックリング法によって、無機電子注入輸送層を形成することが好ましい。多元スパッタリング法によれば、それぞれのターゲットに適した条件で、スパッタリングすることができる。また、第１成分と第２成分の混合ターゲットを用いて、一元スパックリング法によって、無機電子注入輸送層を形成することもできる。
【０１２９】
無機電子注入輸送層をスパックリング法によって形成する場合、スパッタガスの圧力は、０．１〜１パスカルの範囲に設定することが好ましい。スパッタガスとしては、スパッタリング法に、通常、用いられる不活性ガス、たとえば、Ａｒ、Ｎｅ、Ｘｅ、Ｋｒなどを使用することができ、必要に応じて、窒素ガスを用いることもできる。スパッタリング時において、これらのスパッタガスに加えて、１〜９９％の酸素ガスを混合するようにしてもよい。
【０１３０】
スパッタリング法としては、RF電源を用いた高周波スパッタリング法や、DCスパッタリング法を使用することができ、RF電源を用いた高周波スパッタリングの電力は０．１〜１０W／平方センチメートルの範囲が好ましく、成膜速度は０．５〜１０nm／分、とくに、１〜５nmの範囲が好ましい。
【０１３１】
成膜時の基板温度は、２５〜１５０℃程度である。
【０１３２】
本発明において、有機ＥＬ構造体を形成する基板としては、非晶質基板たとえばガラス、石英など、結晶基板たとえば、Ｓｉ、ＧａＡｓ、ＺｎＳｅ、ＺｎＳ、ＧａＰ、ＩｎＰなどがあげられ、またこれらの結晶基板に結晶質、非晶質あるいは金属のバッファ層を形成した基板も用いることができる。また金属基板としては、Ｍｏ、Ａｌ、Ｐｔ、Ｉｒ、Ａｕ、Ｐｄなどを用いることができる。さらに、プラスチック等の樹脂材料、可撓性を有する材料を用いることもできる。基板材料は、好ましくはガラス基板、樹脂材料である。基板は、光取り出し側となる場合、上記電極と同様な光透過性を有することが好ましい。
【０１３３】
ガラス材として、コストの面からアルカリガラスが好ましいが、この他、ソーダ石灰ガラス、鉛アルカリガラス、ホウケイ酸ガラス、アルミノケイ酸ガラス、シリカガラス等のガラス組成のものも好ましい。特に、ソーダガラスで、表面処理の無いガラス材が安価に使用できる。
【０１３４】
さらに、素子の有機層や電極の酸化を防ぐために、素子上を封止板等により封止することが好ましい。封止板は、湿気の侵入を防ぐために、接着性樹脂層を用いて、封止板を接着し密封する。封止ガスは、Ａｒ、Ｈｅ、Ｎ₂ 等の不活性ガス等が好ましい。また、この封止ガスの水分含有量は、１００ppm 以下、より好ましくは１０ppm 以下、特には１ppm 以下であることが好ましい。この水分含有量に下限値は特にないが、通常０．１ppm 程度である。
【０１３５】
封止板の材料としては、上記基板と異なる材料を用いることも可能であるが、好ましくは基板材料と同様のもの、あるいは同等の熱膨張係数、機械強度を有するものである。
【０１３６】
封止板は、スペーサーを用いて高さを調整し、所望の高さに保持してもよい。スペーサーの材料としては、樹脂ビーズ、シリカビーズ、ガラスビーズ、ガラスファイバー等が挙げられ、特にガラスビーズ等が好ましい。なお、封止板に凹部を形成した場合には、スペーサーは使用しても、使用しなくてもよい。
【０１３７】
スペーサーは、予め封止用接着剤中に混入されていても、接着時に混入してもよい。封止用接着剤中におけるスペーサーの含有量は、好ましくは０．０１〜３０wt％、より好ましくは０．１〜５wt％である。
【０１３８】
接着剤としては、安定した接着強度が保て、気密性が良好なものであれば特に限定されるものではないが、カチオン硬化タイプの紫外線硬化型エポキシ樹脂接着剤を用いることが好ましい。
【０１３９】
基板に色フィルター膜や蛍光性物質を含む色変換膜、あるいは誘電体反射膜を用いて発光色をコントロールしてもよい。
【０１４０】
色フィルター膜には、液晶ディスプレイ等で用いられているカラーフィルターを用いれば良いが、有機ＥＬ素子の発光する光に合わせてカラーフィルターの特性を調整し、取り出し効率・色純度を最適化すればよい。
【０１４１】
また、ＥＬ素子材料や蛍光変換層が光吸収するような短波長の外光をカットできるカラーフィルターを用いれば、素子の耐光性・表示のコントラストも向上する。
【０１４２】
また、誘電体多層膜のような光学薄膜を用いてカラーフィルターの代わりにしても良い。
【０１４３】
蛍光変換フィルター膜は、ＥＬ発光の光を吸収し、蛍光変換膜中の蛍光体から光を放出させることで、発光色の色変換を行うものであるが、組成としては、バインダー、蛍光材料、光吸収材料の三つから形成される。
【０１４４】
蛍光材料は、基本的には蛍光量子収率が高いものを用いれば良く、ＥＬ発光波長域に吸収が強いことが望ましい。実際には、レーザー色素などが適しており、ローダミン系化合物・ペリレン系化合物・シアニン系化合物・フタロシアニン系化合物（サブフタロシアニン等も含む）ナフタロイミド系化合物・縮合環炭化水素系化合物・縮合複素環系化合物・スチリル系化合物・クマリン系化合物等を用いればよい。
【０１４５】
バインダーは、基本的に蛍光を消光しないような材料を選べば良く、フォトリソグラフィー・印刷等で微細なパターニングが出来るようなものが好ましい。また、基板上に正孔注入電極と接する状態で形成される場合、正孔注入電極（ＩＴＯ、ＩＺＯ等）の成膜時にダメージを受けないような材料が好ましい。
【０１４６】
光吸収材料は、蛍光材料の光吸収が足りない場合に用いるが、必要のない場合は用いなくても良い。また、光吸収材料は、蛍光性材料の蛍光を消光しないような材料を選べば良い。
【０１４７】
本発明の有機ＥＬ素子は、例えば、図１に示すように基板１／正孔注入電極２／金属層３／絶縁層または抵抗層４／正孔注入輸送層５ａ、発光層５ｂ、電子注入輸送層５ｃを含む有機層／無機電子注入輸送層６／電子注入電極７とが順次積層された構成である。また、基板１側に電子注入電極７が形成されている逆積層としてもよい。積層構成は、要求される性能や仕様などにより最適な積層構成とすればよい。有機層は、正孔注入輸送層、発光層、電子注入輸送層等が積層された複数層構成としてもよいし、発光層に電子注入輸送機能、正孔輸送機能などを持たせた単層構成としてもよい。
【０１４８】
有機ＥＬ素子は、直流駆動やパルス駆動され、また交流駆動も可能である。印加電圧は、通常、２〜３０V 程度である。
【０１４９】
【実施例】
［参考例１］
本参考例で述べる有機ＥＬ素子は、図２に示すように、ガラス基板１上に、正孔注入電極２である透明導電膜ＩＴＯ：１００nmと、正孔注入金属層３であるＰｔ：０．５nmとＧｅＯ₂ ：Ｉｎ₂Ｏ₃ （スパッタターゲット組成、８５：１５ mol％）１nmで構成される無機正孔注入層４と、下記の化１５で示されるジスチリルアリーレン誘導体に同じく下記の化１６で示されるジスチリルアリーレンアミン誘導体が３体積％添加された膜厚が１００nmの有機発光層５と、フッ化リチウム：０．３nmの無機電子注入層６と、マグネシウムに銀が２体積％添加された膜厚が２００nmである電子注入電極７とが順々に積層された構造を有する。
【０１５０】
【化１５】

【０１５１】
【化１６】

【０１５２】
この有機ＥＬ素子の製造方法を具体的に説明する。
【０１５３】
まず、上記の正孔注入電極２が形成されたガラス基板１を１０分間超音波洗浄した後、純水でリンスした。その後オーブンにて１１０℃で８時間以上ベークを行った。このＩＴＯ付基板にＵＶ／Ｏ₃ 洗浄を行った後、真空装置に導入し槽内を１×１０⁴ Pa以下まで減圧した。
【０１５４】
次いで、正孔注入金属層３として、ＰｔをＥＢ蒸着で、蒸着速度を０．０１nm／sec で０．５nm成膜した。このときの条件は、電圧４．６keV 、電流値２００ｍＡとした。
【０１５５】
減圧状態を保ったまま、ターゲットにＧｅＯ₂ ：Ｉｎ₂０₃ （８５：１５ mol％）を用い、無機高抵抗層を膜厚１nm成膜し、正孔注入層を合計膜厚１．５nmに形成した。この時の条件は、スパッタガスに１０％Ｏ₂／Ａｒを用い、圧力：０．１５Pa、投入電力：０．８Ｗ／cm² 、成膜レート：０．０５nm／sec であった。
【０１５６】
さらに減圧を保ったまま、上記化１５の化合物に化１６の化合物を３体積％添加して、蒸着速度：０．１nm／sec として有機発光層５を抵抗加熱法により膜厚１００nmの厚さに蒸着した。
【０１５７】
次いで、フッ化リチウムを抵抗加熱法で蒸着速度０．０１nm／sec として電子注入層６を膜厚０．３nmの厚さに蒸着した。
【０１５８】
さらに、マグネシウムに銀を２体積％添加して、蒸着速度０．１nm／sec として電子注入電極７を膜厚２００nmの厚さに蒸者した。
以上の上程で有機ＥＬ素子を作製した。
【０１５９】
〔参考例２〕
無機高抵抗層を３nmとしＰｔ層０．５nmと合わせて３．５nmの正孔注入層とした以外は参考例１と同様の構造とした。
【０１６０】
〔参考例３〕
有機発光層４をトリス（８一キノリノール）アルミニウム（以下、Ａｌｑ３と略す）を膜厚１００nmで構成した以外は参考例２と同様の構造とした。
【０１６１】
〔実施例１〕
図３に示すように、有機正孔注入層５ａとして、Ｎ，Ｎ’−ジフェニル−Ｎ，Ｎ’−ビス（３−メチルフエニル）−１、１’−ビフェニル−４，４’−ジアミン（ＴＰＤと略す）膜厚２０nmを、無機正孔注入層４と有機発光層５ｂの間に挿入した以外は参考例３と同様の構造とした。
【０１６２】
〔参考例４〕
無機絶縁層をＳｉＯ₂ ：３nmとし、Ｐｔ層：０．５nmと合わせて３．５nmの正孔注入層とした以外は実施例１と同様の構造とした。
【０１６３】
〔比較例１〕
無機正孔注入層を無機高抵抗層ＧｅＯ₂ ：Ｉｎ₂０₃ ：１nmのみとし、Ｐｔ金属層を設けない以外は参考例１と同様の構造とした。
【０１６４】
〔比較例２〕
無機正孔注入層を無機高抵抗層ＧｅＯ₂ ：Ｉｎ₂０₃ ：３nmのみとし、Ｐｔ金属層を設けない以外は参考例２と同様の構造とした。
【０１６５】
〔比較例３〕
無機正孔注入層を無機高抵抗層ＧｅＯ₂ ：Ｉｎ₂０₃ ：３nmのみとし、Ｐｔ金属層を設けない以外は参考例３と同様の構造とした。
【０１６６】
〔比較例４〕
無機正孔注入層を無機高抵抗層ＧｅＯ₂ ：Ｉｎ₂０₃ ：３nmのみとし、Ｐｔ金属層を設けない以外は実施例１と同様の構造とした。
【０１６７】
〔比較例５〕
無機正孔注入層を無機絶縁層ＳｉＯ₂ ：３nmのみとし、Ｐｔ金属層を設けない以外は参考例４と同様の構造とした。
【０１６８】
〔比較例６〕
無機正孔注入層として、Ｐｔの代わりにＭｇを０．５nm成膜し、次に無機高抵抗層ＧｅＯ₂ ：Ｉｎ₂０₃ を３nm成膜し、合わせて３．５nmとした以外は参考例２と同様の構造とした。
【０１６９】
〔比較例７〕
ＩＴＯ上にＧｅＯ₂ ：Ｉｎ₂０₃ 正孔注入層を先に成膜し、その後Ｐｔ層を形成した以外は参考例１と同様にして素子を作製した。
【０１７０】
この素子は、金属層上に有機層を形成する際に、有機層がはじかれてしまい、有機薄膜を均一に形成することができなかった。
【０１７１】
上記参考例１〜４、実施例１および比較例１〜７の各有機ＥＬ素子に、ＩＴＯ電極側をプラス、電子注入電極側をマイナスとして所定の電圧を印加し、電流密度１０mA／cm² となるときの電圧と、輝度１００cd／m² となるときの電圧を測定した。
【０１７２】
結果を下記表１に示す。
【０１７３】
【表１】

【０１７４】
また、上記実施例、参考例で使用した絶縁層、高抵抗層の抵抗率の実測値を以下に示す。測定は、サンプルを所定面積となるようにマスキングしたものを、ＩＴＯ透明電極とＡｌ電極で挟み込み、印加電圧と電流から求めた。なお、測定値は環境の湿度や、ノイズレベルの影響を受けやすく、誤差を含んだ値であると考えられる。
【０１７５】
【表２】

【０１７６】
上記結果から、参考例１〜４と比較例１〜５と実施例１について、それぞれ対応するサンプル、例えば、参考例１（駆動電圧６．６Ｖ、１０mA／cm² 時）と比較例１（駆動電圧１２．６Ｖ、１０mA／cm² 時）とを比較すると、本発明サンプルは駆動電圧の低下が顕著であることがわかる。なお、比較例３では輝度１００cd／m² となるときの電圧を測定使用としたところ、測定する前に素子が破壊してしまった。
【０１７７】
一方、仕事関数がＩＴＯ（仕事関数４．６eV）よりも低いマグネシウム（仕事関数３．６eV）をＰｔ（仕事関数５．４eV）の代わりに挿入しても、比較例６の結果から、駆動電圧の低下は見られなかった。
【０１７８】
比較例７では輝度が得られず、輝度１００cd／m² となるときの電圧駆動電圧は測定できなかった。これは、おそらく最初にリーク部が焼き切れるため、その後駆動電圧が異常に上昇したものと考えられる。また、発光部での輝度ムラもひどく、輝点が観測された。
【０１７９】
以上の結果から、正孔注入電極よりも高い仕事関数を有する金属を挿入することによって、駆動電圧が低下することが明かとなった。
【０１８０】
〔参考例５〕
参考例１と比較例１の素子について、アルゴン雰囲気にて電流密度１００mA／cm² の定電流により連続発光させ、各有機ＥＬ素子の寿命を測定した。結果を図４に示す。
【０１８１】
上記結果より、参考例１における有機ＥＬ素子の発光輝度低下の進行は、比較例１よりも格段に遅い事が分かった。これは高抵抗層の挿入によるリーク抑制と、金属層挿入による駆動電圧の低下に伴う発熱量の減少によるものであると考えられる。
【０１８２】
以上説明したとおり、本発明によれば、高い仕事関数を有する金属層と絶縁層あるいは高抵抗層を無機正孔注入層として用いることにより、リークの抑制と、それに加えて絶縁層と有機層とのエネルギー障壁を小さくすることで、素子の駆動電圧を低く、かつ素子の長寿命化が達成できる。よって本発明は有機ＥＬ素子の各種表示デバイスへの応用が可能となり、その効果は大きい。
【０１８３】
【発明の効果】
以上のように本発明によれば、絶縁層あるいは抵抗層を正孔注入層に用いたときに得られる素子リーク抑制等の素子信頼性を有し、さらに、その短所である駆動電圧の上昇を防ぎ、信頼性が高く駆動電圧が低い有機ＥＬ素子を提供することができる。
【図面の簡単な説明】
【図１】本発明の有機ＥＬ素子の基本構成を示す概略断面図である。
【図２】参考例１の有機ＥＬ素子の基本構成を示す概略断面図である。
【図３】実施例１の有機ＥＬ素子の基本構成を示す概略断面図である。
【図４】参考例５の寿命特性の測定結果を示したグラフである。
【符号の説明】
１ 基板
２ 正孔注入電極
３ 金属層
４ 絶縁層／抵抗層
５ 有機層
５ａ 正孔注入輸送層
５ｂ 発光層
５ｃ 電子注入輸送層
６ 無機電子注入層
７ 電子注入電極[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic electroluminescence element (organic EL element) using an organic material that emits light by recombination of holes and electrons.
[0002]
[Prior art]
In recent years, a demand for a flat panel display has been increased from the viewpoint of reducing an occupied area, and a device using an electroluminescence element (hereinafter abbreviated as an EL element) that is lightweight and does not require a backlight has been attracting attention. The EL element includes an organic EL element and an inorganic EL element. Among these, unlike the inorganic EL element, the organic EL element has an advantage that it can be driven at a low voltage of about 20V.
[0003]
The structure of the organic EL element is a two-layer structure having a hole injection transport layer and an organic light emitting layer / electron injection transport layer between the hole injection electrode and the electron injection electrode, or an organic light emitting layer / hole injection transport. For example, a two-layer structure having a layer and an electron injecting and transporting layer can be used.
[0004]
Moreover, as a structure of two or more layers, there is one having a hole injection transport layer, an organic light emitting layer, and an electron injection transport layer. Or the single layer structure which has a light emitting layer, a positive hole injection transport layer, and an electron injection transport layer in one layer is also known.
[0005]
In these organic EL elements, in order to obtain practical luminance with practical electric power, an injection layer for efficiently injecting and transporting holes and electrons to the organic light emitting layer is required as in the structure described above.
[0006]
Examples of techniques that have been disclosed so far in order to produce highly efficient organic EL elements include the following.
[0007]
Japanese Patent Application Laid-Open No. 6-5369 discloses a method of manufacturing an organic EL element having high efficiency by laminating a metal having a work function larger than that of ITO in contact with the hole injection electrode ITO and lowering an injection barrier to the organic layer. Is published. However, Pt, Au, and the like shown here as metals having a work function larger than that of ITO have poor bondability with the organic layer, so that film peeling easily occurs at the interface between the metal film and the organic film. The problem is that the reliability such as the lifetime becomes extremely low.
[0008]
Japanese Patent Application Laid-Open No. 9-63771 discloses an attempt to lower the driving voltage by inserting a metal oxide thin film having a large work function between the anode and the organic compound to reduce the energy gap with the organic compound. By using a metal oxide, the problem of deterioration of the bonding property can be avoided. However, in this method, since the metal oxide thin film is conductive, there is a problem that current leakage of the element cannot be prevented, and the reliability is also lowered.
[0009]
The hole injecting and transporting layer in contact with the ITO is usually made of an organic material, but the organic material used for the organic EL element is relatively expensive and has a problem in terms of manufacturing cost. For this reason, there is also an object of suppressing element leakage, and attempts have been made to replace the hole injecting and transporting layer with an inorganic material such as an inorganic insulating layer or an inorganic high resistance layer that is inexpensive and has high leakage resistance.
[0010]
For example, JP-A-8-288069 reports a method for suppressing leakage and short-circuiting of an organic EL element by inserting an insulating thin film layer between an anode and a cathode and an organic compound. Although this method has an effect on the device life, on the other hand, since the insulating layer has a low hole injection function, the drive voltage rises and the advantage of the organic EL device that it is low voltage drive can be utilized. In addition, power consumption increases.
[0011]
Similarly, in order to solve the problem of leakage, Japanese Patent Application Laid-Open No. 11-162646 attempts to insert a dielectric thin film layer. The example of this publication shows a decrease in driving voltage, but in the structure of this publication, the dielectric thin film layer is essential on both the hole injection layer side and the electron injection layer side. As described, when the dielectric thin film layer is disposed only on the hole injection layer side, the drive voltage is increased. That is, it is considered that the voltage drop effect is not effective on the hole injection layer, and is a result of the voltage drop due to the arrangement of the alkali metal on the electron injection layer side.
[0012]
In addition, in Japanese Patent Application Laid-Open No. 2000-100555, an inorganic insulating hole injection layer is arranged, and this hole injection layer contains Cu, Fe, Ni, Ru, Sn, Au and inorganic insulating hole injection. Increasing the injectability of the layer is disclosed. However, the inclusion of a conductor in the insulating layer results in a low resistance film when the content is large, which adversely affects leakage suppression. When the content is small, the hole injection property is similar to that of JP-A-8-288069. It becomes a trade-off relationship that the drive voltage increases and the drive voltage increases, and it is difficult to establish both simultaneously. Furthermore, since these metals have a higher or lower work function than that of ITO, there is no way to combine the work functions.
[0013]
[Problems to be solved by the invention]
It is an object of the present invention to have element reliability such as element leakage suppression obtained when an insulating layer or a resistance layer is used for a hole injection layer, and to prevent an increase in driving voltage, which is a disadvantage of the element reliability. An organic EL element having a high driving voltage and a low driving voltage is provided.
[0014]
[Means for Solving the Problems]
A metal layer having a high work function is provided between the anode and the organic layer, and an insulating layer is provided between the metal and the organic layer. By the action of the high work function metal, the injection property into the organic layer is improved, the driving voltage is lowered, and the leakage is suppressed by arranging the insulating layer.
[0015]
  That is, the above object is achieved by the following configuration of the present invention.
(1) A metal layer containing a metal element having a work function larger than that of the hole injection electrode between a pair of electrodes including a hole injection electrode and an electron injection electrode from the hole injection electrode side to the electron injection electrode , Having an organic layer including an inorganic hole injection layer and a light emitting layer in this order,The organic layer including the light emitting layer has a hole injection transport layer made of an organic compound between the inorganic hole injection layer and the light emitting layer,The inorganic hole injection layer is formed of GeO formed on the metal layer by a sputtering method.₂And In₂O_ThreeAn organic EL element characterized by being a layer comprising:
(2) The organic EL device according to (1), wherein the metal layer contains one or more elements selected from Pt, Au, Pd, Ni, Re, Co, Se, and Ir.
(3) The organic EL device according to (1) or (2), wherein the metal layer has a thickness of 0.1 to 2 nm.
(4) The metal layer is made of platinum and has a thickness of about 0.5 nm, and the GeO₂And In₂O_ThreeThe organic EL device according to the above (3), wherein the inorganic hole injection layer comprising 1 to 3 has a thickness of 1 to 3 nm.
(5) The organic EL element according to any one of the above (1) to (4), wherein the hole injection electrode, the metal layer, and the insulating layer or the resistance layer have a light transmittance of 80% or more.
[0016]
Here, the insulating layer has a specific resistance of 10⁸ It is a layer containing a material of Ω · cm or more, and the resistance layer has a specific resistance of 10⁸ ・ Cm-10^-2 A layer having a material in the cm range. The definition of the insulating layer is, for example, S.I. M.M. Jee's book, “Semiconductor Device”, Sangyo Tosho Co., Ltd., 1987. The specific resistance range in the resistance layer has a specific resistance equal to or lower than that of the insulating layer, and preferably has a specific resistance equal to or higher than the organic material used in the organic EL element, and the above range is preferable.
[0017]
As a material constituting the insulating layer in the organic EL element in the present invention, for example, those described in JP-A-8-288069 can be used. Specifically, AIN, BN, GaN, Li_ThreeN, Si_ThreeN_Four , Nitrides such as TaN and TiN, Al₂0_Three , BaO, CaO, Fe₂0_Three , GeO, GeO₂ MgO, NiO, SiO, SiO₂ , TiO, TiO₂ , Ti₂0_Three , Y₂0_Three Oxides such as CuS, EuS, GeS, SnS, SrS and ZnS, carbides such as SiC and TiC, AIF, BaF₂ , FeF_Three , LiF, MgF₂ Fluoride such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polystyrene, polycarbonate, polyurethane, polyimide and the like can be used.
[0018]
The insulating layer is preferably silicon oxide, which is known as a good insulating film. Further, germanium oxide or silicon nitride may be used. The insulating layer preferably has a higher resistance value than the organic layer, but may be a resistor in which indium oxide as a conductor is added to germanium oxide as an insulator.
[0019]
As a method for forming the insulating layer, a sputtering method, a vacuum evaporation method, an EB evaporation method, a CVD method, and the like are conceivable. However, the sputtering method is preferable because the film quality can be easily controlled and the apparatus can be easily maintained.
[0020]
When the insulating layer is formed by a sputtering method, when a metal oxide is used for the insulating layer, an inert atmosphere such as nitrogen or Ar is possible, but it is more preferable to add oxygen to the atmosphere to supplement oxygen. As a result, the denseness is improved.
[0021]
Moreover, as a resistance layer, the following formula,
(Si_1-xGe_x) O_y
[However, 0 ≦ x ≦ 1, 1.7 ≦ y ≦ 2.2]
Examples of the main component represented by the formula (1) include those containing a conductor such as Cu, Fe, Ni, Ru, Sn, Au, or In. In the present invention, a resistive layer is preferable to the insulating layer.
[0022]
The main component of the resistance layer is
(Si_1-xGe_x) O_yIn
0 ≦ x ≦ 1,
1.7 ≦ y ≦ 2.2, preferably 1.85 ≦ y ≦ 2.1
It is. The resistance layer may be silicon oxide or germanium oxide, or a mixed thin film thereof. Even if y is larger and silicon or germanium has less vacancies, the hole injection function is lowered even if y is smaller and oxygen vacancies are larger. The composition of the resistance layer may be examined by Rutherford backscattering or chemical analysis, for example.
[0023]
The resistance layer contains one or more of Cu, Fe, Ni, Ru, Sn, and Au as subcomponents. Among them, it is preferable to contain Sn, Ni, Cu, particularly Ni. The content of these elements is 10 at% or less in total, more preferably 0.05 to 10 at%, further preferably 0.1 to 10 at%, particularly 0.5 to 5 at%. When the content exceeds this, the hole injection function is lowered.
[0024]
In addition, the resistance layer may contain, as impurities, H, Ne, Ar, Kr, Xe, or the like used for sputtering gas in total of 5 at% or less.
[0025]
In addition, if it is such a composition as an average value of the whole resistance layer, it may not be uniform and it may be a structure having a concentration gradient in the film thickness direction.
[0026]
The resistance layer is usually in an amorphous state.
[0027]
The thickness of the resistance layer is not particularly limited, but is preferably about 0.1 to 10 nm, particularly about 1 to 10 nm. Even if the high resistance layer is thinner or thicker, hole injection cannot be performed sufficiently.
[0028]
As a method for manufacturing the resistance layer, various physical or chemical thin film forming methods such as a sputtering method and an EB vapor deposition method can be considered, and a sputtering method is preferable.
[0029]
When the resistance layer is formed by sputtering, the sputtering gas pressure during sputtering is preferably in the range of 0.1 to 1 Pa. As the sputtering gas, an inert gas used in a normal sputtering apparatus, such as Ar, Ne, Xe, or Kr, can be used. If necessary, N₂ May be used. As an atmosphere during sputtering, in addition to the above sputtering gas, O₂ Reactive sputtering may be performed by mixing about 1 to 99%. The above oxide may be used as a target, and single or multi-source sputtering may be used.
[0030]
As the sputtering method, a high-frequency sputtering method using an RF power source, a DC sputtering method, or the like can be used, but RF sputtering is particularly preferable. The power of the sputtering apparatus is preferably 0.1 to 10 W / cm by RF sputtering.² The film forming rate is preferably 0.5 to 10 nm / min, particularly preferably 1 to 5 nm / min.
[0031]
The substrate temperature during film formation is about room temperature (25 ° C.) to about 150 ° C.
[0032]
In the present invention, a metal metal layer having a higher work function than the hole injection electrode is provided between the hole injection electrode and the insulating layer or the resistance layer. By providing a metal layer having a higher work function than that of the hole injection electrode between the hole injection electrode and the insulating layer / resistance layer, it is possible to prevent an increase in driving voltage associated with the insulating layer / resistance layer. . Furthermore, the occurrence of leakage and dark spots is reduced by having the insulating layer / resistive layer.
[0033]
At this time, if the hole injection electrode is an ITO film (work function 4.6 eV), the metal layer preferably contains a metal element having a work function higher than that of the ITO film. By using a material having a work function higher than that of the hole injection electrode, hole injection efficiency can be increased, and a voltage drop in the insulating layer and the resistance layer can be suppressed. Further, since the hole injection electrode and the metal layer are conductors, even if the work function of the metal layer is higher than that of the hole injection electrode, ohmic connection is not a problem.
[0034]
Specific examples of the material constituting the metal layer include Ir (4.7 eV), Se (4.72 eV), Co (4.97 eV), Re (5.0 eV), Ni (5.15 eV), Pd. It is preferable to contain one or more elements selected from (5.17 eV), Au (5.2 eV), and Pt (5.43 eV). The mixing ratio when using two or more of these elements is arbitrary. These metal elements are desirably elements that substantially constitute the metal layer, excluding inevitable components mixed in from materials, manufacturing processes, and the like.
[0035]
If the use of the present invention is considered as a display and light is extracted from the ITO side, the metal layer is desirably transparent, and the transmittance is preferably 80% or more. For example, in the case of Pt, the film thickness is 1 nm and the transmittance is 82%, and the film thickness is preferably 1 nm or less, particularly preferably 0.1 to 1 nm. When the film thickness is thinner than 0.1 nm, it becomes difficult to obtain the effect of providing the high work function metal layer.
[0036]
As a method for forming the metal layer, a vacuum vapor deposition method, an EB vapor deposition method, a sputtering method, or the like can be considered, but a sputtering method capable of increasing the adhesion between ITO and the metal layer is preferable.
[0037]
Also, if the stacking order of the metal layer and the insulating layer / resistive layer is the insulating layer / resistive layer, metal layer, and organic layer from the hole injection electrode side, the adhesion between the metal layer and the organic layer becomes a problem, and leakage occurs. Element characteristics such as the occurrence of the above are deteriorated. Therefore, the metal layer and the insulating layer / resistive layer are stacked in the order of the metal layer, the insulating layer / resistive layer, and the organic layer from the hole injection electrode side, and the organic layer and the metal layer are not in direct contact with each other. It is good.
[0038]
The hole injection electrode material is preferably one that can efficiently inject holes into a hole injection layer or the like, and a substance having a work function of 4.5 eV to 5.5 eV is preferable. Specifically, tin-doped indium oxide (ITO), zinc-doped indium oxide (IZO), indium oxide (In₂O_Three), Tin oxide (SnO)₂) And zinc oxide (ZnO) are preferred. These oxides may deviate somewhat from their stoichiometric composition. In₂O_ThreeFor SnO₂Is preferably 1 to 20 wt%, more preferably 5 to 12 wt%. Also, In at IZO₂O_ThreeThe mixing ratio of ZnO to is usually about 12 to 32 wt%.
[0039]
The electrode on the light extraction side preferably has a light transmittance of 50% or more, more preferably 80% or more, and particularly preferably 90% or more with respect to light having a light emission wavelength band, usually 400 to 700 nm. If the transmittance is too low, light emission from the light emitting layer itself is attenuated, and it becomes difficult to obtain luminance necessary for the light emitting element.
[0040]
The thickness of the electrode is preferably 50 to 500 nm, particularly 50 to 300 nm. Further, the upper limit is not particularly limited, but if it is too thick, there is a concern about a decrease in transmittance or peeling. If the thickness is too thin, a sufficient effect cannot be obtained, and there is a problem in terms of film strength at the time of manufacture.
[0041]
As the inorganic electron injecting and transporting layer, the following can be used as necessary as having an electron injecting property in combination with an organic electron injecting and transporting layer and the like. For example, metal elements such as K, Li, Na, Mg, La, Ce, Ca, Sr, Ba, Sn, Zn, Zr, etc., or a two-component or three-component alloy system containing them to improve stability For example, Ag · Mg (Ag: 0.1 to 50 at%), Al·Li (Li: 0.01 to 14 at%), In · Mg (Mg: 50 to 80 at%), Al · Ca (Ca: 0. 01-20 at%) and the like.
[0042]
The thickness of the inorganic electron injecting and transporting layer may be a certain thickness or more that can sufficiently inject electrons, and may be 0.1 nm or more, preferably 0.5 nm or more, particularly 1 nm or more. Moreover, although there is no restriction | limiting in particular in the upper limit, Usually, a film thickness should just be about 1-500 nm.
[0043]
The inorganic electron injecting and transporting layer may be an inorganic layer mainly composed of a semiconductor element such as Si or Ge, or an alkali metal salt such as lithium fluoride disclosed in Japanese Patent Application Laid-Open No. 9-17574 may be formed to about 1 nm. A film may be formed.
[0044]
The electron injecting electrode does not need to be particularly limited in combination with the inorganic electron injecting and transporting layer and need not have electron injecting properties with a low work function, and an ordinary metal can be used. Among them, in terms of conductivity and ease of handling, Al, Ag, In, Ti, Cu, Au, Mo, W, Pt, Pd and Ni, particularly one or two selected from Al and Ag, etc. Metal elements are preferred.
[0045]
The thickness of these electron injection electrodes may be a certain thickness or more that can give electrons to the inorganic electron injection and transport layer, and may be 50 nm or more, preferably 100 nm or more. The upper limit is not particularly limited, but the normal film thickness may be about 50 to 500 nm.
[0046]
Further, when a protective layer is provided in order to protect the organic EL element from moisture in the atmosphere, deterioration due to the generation of a dark spot (referred to as a dark spot) generated in the element can be suppressed. The protective film is made of SiN, SiON, SiO₂ , Al₂O_Three A film having a high water blocking ability is preferred.
[0047]
As a method for forming the protective film, a vapor deposition method, a sputtering method, a CVD method, or the like can be considered, but a plasma CVD method that can be formed at a low temperature and has good step coverage is preferable.
[0048]
Moreover, it is preferable to form a protective film without exposing the element to the atmosphere after the organic EL element is manufactured. The thickness of the protective film is not particularly limited, but is preferably 100 to 5000 nm. If the thickness of the protective film is thinner than this, the water blocking ability is lowered, and if it is thicker than this, the film peeling due to the stress of the protective film and the characteristics of the organic EL element are affected.
[0049]
The total thickness of the electron injection electrode and the protective layer is not particularly limited, but is usually about 50 to 500 nm.
[0050]
Next, the organic layer of the organic EL element will be described in detail.
[0051]
The organic EL device according to the present invention includes at least one organic light emitting layer between two electrodes, at least one of which is transparent, and the organic light emitting layer includes at least one or two kinds of compounds involved in the light emitting function. It is out.
[0052]
In the organic EL device according to the present invention, the wavelength of light emitted from at least one organic light emitting layer is not particularly limited, but preferably, at least one organic light emitting layer continuously emits light of at least 380 to 780 nm. It is configured to emit white light having a spectrum.
[0053]
In the present invention, it is particularly preferable that at least one organic light emitting layer is configured to emit white light having a continuous light emission spectrum of 430 nm to 650 nm or less.
[0054]
In the present invention, the organic light emitting layer includes a host material which is a hole transporting compound, an electron transporting compound, or a mixture thereof, and serves to inject holes and electrons, to transport holes and electrons, and to holes and electrons. It preferably has a function of generating excitons by recombination, and contains an electronically relatively neutral compound.
[0055]
The hole transporting compound used as a host material for the organic light emitting layer includes triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, virazoline derivatives, virazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcones. Derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, and stilbene derivatives are exemplified, and triphenyldiamine derivatives can be preferably used.
[0056]
As an example of the triphenyldiamine derivative, a tetraarylpendicine compound (triaryldiamine or triphenyldiamine: TPD) is particularly preferable.
[0057]
Preferred specific examples of the tetraarylbendicine compound (TDP) are as follows.
It is.
[0058]
[Chemical 1]

[0059]
[Chemical 2]

[0060]
[Chemical Formula 3]

[0061]
As the electron transporting compound used as the host material of the organic light emitting layer, a quinoline derivative can be preferably used, and further, a metal complex having 8-quinolinol or a derivative thereof as a ligand, particularly a structure of the following formula Tris (8-quinolinato) aluminum (Alq3) having the following is preferably used. In addition, phenylanthracene derivatives and tetraarylethene derivatives can also be used as the electron transporting compound.
[0062]
[Formula 4]

[0063]
In the present invention, the organic light emitting layer preferably has a structure in which a host material that is a hole transporting compound, an electron transporting compound, or a mixture thereof is doped with a fluorescent dopant.
[0064]
In addition, the organic EL device according to the present invention preferably includes two organic light emitting layers stacked on each other. When two organic light-emitting layers are formed, a wide light emission wavelength band is secured by doping with fluorescent materials having different light emission wavelengths, and the degree of freedom of color of light emission color is improved. be able to.
[0065]
In the present invention, the fluorescent substance to be contained as a dovant is, for example, a compound disclosed in JP-A 63-264692, specifically, a rubrene-based compound, a coumarin-based compound, a quinacridone-based compound, a dicyanomethylbilane-based compound. One or more compounds selected from the group consisting of compounds such as compounds can be preferably used.
[0066]
Examples of fluorescent substances that can be preferably used in the present invention are as follows.
[0067]
[Chemical formula 5]

[0068]
[Chemical 6]

[0069]
[Chemical 7]

[0070]
[Chemical 8]

[0071]
Furthermore, in the present invention, the naphthacene compounds described in JP-A-2000-26334 and JP-A-2000-26337 can also be preferably used as fluorescent substances to be contained as dovants. In addition, when used in combination with a coumarin compound, a quinacridone compound, a dicyanomethylpyran compound, etc., the lifetime of the organic EL device can be improved drastically.
[0072]
In the present invention, a naphthacene compound that can be preferably used as a fluorescent substance to be contained as a dovant has a basic skeleton represented by the formula (I).
[0073]
[Chemical 9]

In formula (I), R¹ ~ R^Four Each represents an unsubstituted or substituted alkyl group, aryl group, amino group, heterocyclic group or alkenyl group. Moreover, it is preferably any of an aryl group, an amino group, a heterocyclic group, and an alkenyl group.
[0074]
R¹ ~ R^Four The aryl group represented by may be monocyclic or polycyclic, and includes condensed rings and ring assemblies. The total carbon number is preferably 6 to 30, and may have a substituent.
[0075]
R¹ ~ R^Four As the aryl group represented by, preferably a phenyl group, (o-, m-, p-) tolyl group, pyrenyl group, perylenyl group, coronenyl group, (1- and 2-) naphthyl group, anthryl group, (O-, m-, p-) biphenylyl group, terphenyl group, phenanthryl group and the like.
[0076]
R¹ ~ R^Four The amino group represented by may be any of alkylamino group, arylamino group, aralkylamino group and the like. These preferably have an aliphatic group having 1 to 6 carbon atoms in total and / or an aromatic carbocyclic ring having 1 to 4 rings. Specific examples include a dimethylamino group, a diethylamino group, a dibutylamino group, a diphenylamino group, a ditolylamino group, a bisdiphenylylamino group, and a bisnaphthylamino group.
[0077]
R¹ ~ R^Four Examples of the heterocyclic group represented by the formula include a 5-membered or 6-membered aromatic heterocyclic group containing O, N, S as a hetero atom, and a condensed polycyclic aromatic heterocyclic group having 2 to 20 carbon atoms. Can be mentioned.
[0078]
R¹ ~ R^Four Are represented by (1- and 2-) phenylalkenyl groups, (1,2-, and 2,2-) diphenylalkenyl groups having a phenyl group as at least one substituent, (1 , 2,2-) triphenylalkenyl group and the like are preferable, but may be unsubstituted.
[0079]
Examples of the aromatic heterocyclic group and the condensed polycyclic aromatic heterocyclic group include a thienyl group, a furyl group, a pyrrolyl group, a pyridyl group, a quinolyl group, and a quinoxalyl group.
[0080]
R¹ ~ R^Four When has a substituent, at least two of these substituents are preferably any of an aryl group, an amino group, a heterocyclic group, an alkenyl group, and an aryloxy group. For the aryl group, amino group, heterocyclic group and alkenyl group, the above R¹ ~ R^Four It is the same.
[0081]
R¹ ~ R^Four As the aryloxy group serving as a substituent, a group having an aryl group having 6 to 18 carbon atoms is preferable, and specifically, an (o-, m-, p-) phenoxy group or the like.
[0082]
Two or more of these substituents may form a condensed ring. Further, it may be further substituted, and preferred substituents in that case are the same as described above.
[0083]
R¹ ~ R^Four When has a substituent, it is preferable that at least two or more of them have the substituent. The substitution position is not particularly limited, and may be any of meta, para, and ortho positions. R¹ And R^Four , R² And R^Three Are preferably the same, but they may be different.
[0084]
R¹ ~ R⁸ At least 5 or more, more preferably 6 or more of them are unsubstituted, substituted, or substituted alkyl groups, aryl groups, amino groups, alkenyl groups, or heterocyclic groups.
[0085]
R^Five , R⁶ , R⁷ And R⁸ Each represents hydrogen or an alkyl group, aryl group, amino group and alkenyl group which may have a substituent.
[0086]
R^Five , R⁶ , R⁷ And R⁸ As the alkyl group represented by formula (1), those having 1 to 6 carbon atoms are preferable, which may be linear or branched. Preferable specific examples of the alkyl group include methyl group, ethyl group, (n, i) propyl group, (n, i, sec, tert) -butyl group, (n, i, neo, tert) -pentyl group and the like. Can be mentioned.
[0087]
R^Five , R⁶ , R⁷ And R⁸ As the aryl group, amino group and alkenyl group represented by¹ ~ R^Four It is the same as the case of. R^Five And R⁶ , R⁷ And R⁸ Are preferably the same, but they may be different.
[0088]
In the present invention, examples of compounds that can be preferably used as the fluorescent substance to be contained as dovant include the following.
[0089]
[Chemical Formula 10]

[0090]
Embedded image

[0091]
When two organic light emitting layers are provided, it is preferable that each organic light emitting layer includes two or more kinds of these fluorescent substances, and the two or more kinds of fluorescent substances have different emission wavelengths.
[0092]
In the present invention, the content of the dopant in the organic light emitting layer is preferably 0.01 to 20% by weight, and more preferably 0.1 to 15% by weight.
[0093]
In the present invention, the thickness of the organic light emitting layer is not particularly limited, and the preferred thickness varies depending on the forming method, but is usually 5 to 500 nm, more preferably 10 to 300 nm.
[0094]
In the present invention, when forming two or more organic light emitting layers, the thickness of each organic light emitting layer is in a range from the thickness corresponding to one molecular layer to less than the total thickness of the organic light emitting layer. Specifically, it is 1 to 85 nm, preferably 5 to 60 nm, and more preferably 5 to 50 nm.
[0095]
In the present invention, the organic light emitting layer is preferably formed by vapor deposition.
[0096]
In the present invention, the conditions for forming the organic light emitting layer by vapor deposition are not particularly limited, but are 1 × 10 5.^-FourIt is preferable that the steaming speed is about 0.01 to 1 nm / second below Pascal.
[0097]
In the present invention, preferably, the organic light emitting layer contains a mixture of a hole transporting compound and an electron injecting and transporting compound.
[0098]
When the organic light emitting layer contains a mixture of a hole transporting compound and an electron injecting and transporting compound, a carrier hopping conduction path is formed, so that each carrier moves in a polar dominant substance. Therefore, carrier injection with the opposite polarity is less likely to occur, and therefore, the compound contained in the organic light emitting layer is prevented from being damaged, so that there is an advantage that the lifetime of the device can be improved.
[0099]
Furthermore, by including a dopant made of a fluorescent material in an organic light emitting layer containing a mixture of a hole transporting compound and an electron injecting and transporting compound, the emission wavelength characteristic of the organic light emitting layer itself can be changed, It is possible to shift the emission wavelength to the longer wavelength side, improve the emission intensity, and further improve the stability of the organic EL element.
[0100]
When the organic light emitting layer contains a mixture of a hole transporting compound and an electron injecting and transporting compound, the mixing ratio of the hole transporting compound and the electron injecting and transporting compound depends on each carrier mobility and carrier concentration. Generally, it is generally 1/99 to 99/1, preferably 10/90 to 90/10, more preferably 20/80 to 80/20, most preferably 40, by weight. / 60-60 / 40 is selected.
[0101]
In the case of forming an organic light emitting layer containing a mixture of a hole transporting compound and an electron injecting and transporting compound, the hole transporting compound and the electron injecting and transporting compound are placed in different evaporation sources, evaporated, and co-evaporated. Although it is preferable to write, when the vapor pressures of the hole transporting compound and the electron injection / transporting compound are approximately the same or very close to each other, they can be mixed in advance in the same vapor deposition source and steamed.
[0102]
When forming an organic light emitting layer containing a mixture of a hole transporting compound and an electron injecting and transporting compound, the hole transporting compound and the electron injecting and transporting compound must be uniformly mixed in the organic light emitting layer. Although preferred, it is not always necessary to mix uniformly.
[0103]
In the present invention, the organic layer is preferably a hole transport layer having a function of stably transporting holes in addition to at least one organic light emitting layer, and an electron having a function of stably transporting electrons. It has a transport layer. By providing these layers, it is possible to increase the number of holes and electrons injected into the organic light emitting layer and confine them in the organic light emitting layer, optimize the recombination region, and improve the light emission efficiency. .
[0104]
In the present invention, compounds that can be preferably used in the hole transport layer include, for example, tetraarylbenzidine compounds (triaryldiamine or triphenyldiamine: TPD), aromatic tertiary amines, hydrazone derivatives, carbazole derivatives. , Triazole derivatives ”, imidazole derivatives, oxadiazole derivatives having amino groups, polythiophene, and the like. Of these, tetraarylbendicine compounds (triaryldiamine or triphenyldiamine: TPD) and triarylamine multimers (ATP) described in WO / 98/30071 can be particularly preferably used. .
[0105]
Preferred specific examples of the triarylamine multimer (ATP) are as follows.
[0106]
Embedded image

[0107]
Embedded image

[0108]
Embedded image

[0109]
In the present invention, further, JP-A-63-295695, JP-A-2-191694, JP-A-3-792, JP-A-5-234681, JP-A-5-239455, Various organic compounds described in JP-A-5-299174, JP-A-7-126225, JP-A-7-126226, JP-A-8-100172, EPO650955Al, and the like are also used for the hole injection transport layer. It can be used for a hole injection layer and a hole transport layer.
[0110]
In the present invention, two or more of these compounds may be used in combination, and when two or more of these compounds are used in combination, they may be mixed in one layer or laminated as two or more layers. May be.
[0111]
In the present invention, the hole transport layer can be formed by evaporating the compound. In the case of forming an element by vapor deposition, a uniform thin film of about 1 to 10 nm without pinholes can be formed. Therefore, a compound that has a small ionization potential and absorbs light of visible wavelength is used in the hole injection layer. Even if it is used, it is possible to prevent a decrease in luminous efficiency due to a change in color tone or reabsorption of the emitted color.
[0112]
In the present invention, examples of compounds that can be preferably used in the electron transport layer include, for example, organometallic complexes such as tris (8-quinolinolato) aluminum (Alq3) or derivatives thereof having a ligand of quinolinol or a derivative thereof. A diazole derivative, a perylene derivative, a pyridine derivative, a pyrimidine derivative, a quinoxaline derivative, and the like can be given.
[0113]
In the present invention, the electron transport layer can be formed by evaporating the compound.
[0114]
In the present invention, the conditions for forming the organic light-emitting layer, the hole injection transport layer or the hole injection layer and the hole transport layer, and the electron injection transport layer or the electron injection layer and the electron transport layer by vapor deposition are particularly limited. 1x10, though not^-FourThe deposition rate is preferably about 0.01 to 1 nm / second below Pascal. Each layer is 1x10^-FourIt is preferably formed continuously under reduced pressure below Pascal. 1 × 10^-FourBy forming each layer continuously under reduced pressure below Pascal, it is possible to prevent impurities from being adsorbed on the interface of each layer, so that it becomes possible to obtain a high-performance organic EL element. The drive voltage of the organic EL element can be reduced, and the generation and growth of dark spots can be suppressed.
[0115]
In the present invention, when two or more kinds of compounds are contained in the organic light emitting layer, the hole transport layer, and the electron transport layer, the temperature of each boat containing the compounds is individually controlled, and organic light emission is performed by co-evaporation. It is preferable to form a layer, a hole transport layer, an electron injection transport layer, an electron injection layer, or an electron transport layer.
[0116]
In the present invention, instead of or in addition to the electron transport layer, a high-resistance inorganic electron injecting and transporting layer having an electron conduction path and having a function of blocking holes may be provided.
[0117]
Thus, by providing a high-resistance inorganic electron injecting and transporting layer having an electron conduction path and a function of blocking holes, the organic light emitting layer has electrons in the organic light emitting layer and the electron injection electrode. Can be efficiently injected, the luminous efficiency can be improved, and the drive voltage can be lowered. Furthermore, by providing a high-resistance inorganic electron injecting and transporting layer that has an electron conduction path and has a function of blocking holes, the thickness of the organic EL display panel and the organic EL element can be reduced. Accordingly, it is possible to further reduce the thickness of the organic EL display panel and the organic EL element that are thinned by forming a color filter layer or a color filter.
[0118]
The high resistance inorganic electron injecting and transporting layer preferably has a work function of 4 eV or less, more preferably 1 to 4 eV as the first component,
Preferably one or more alkali metal elements selected from Li, Na, K, Rb, Cs and Fr, or
Preferably one or more alkaline earth metal elements selected from Mg, Ca and Sr, or
Preferably, it contains an oxide of one or more lanthanoid elements selected from La and Ce. Among these, lithium oxide, magnesium oxide, calcium oxide, and cerium oxide are particularly preferable. The mixing ratio in the case of mixing and using these is arbitrary. In these mixtures, lithium oxide is Li₂It is preferably contained in an amount of 50 mol% or more in terms of O.
[0119]
The inorganic electron injection layer further contains one or more elements selected from Zn, Sn, V, Ru, Sm, and In as the second component. In this case, the content of the second component is preferably 0.2 to 40 mol%, more preferably 1 to 20 mol%. When this content is small, the electron injection function is lowered, and when the content is increased, the hole blocking function is lowered. When using 2 or more types together, it is preferable to make total content into said range. The second component may be in a metal element state or an oxide state.
[0120]
As described above, one or more elements selected from the group consisting of Zn, Sn, V, Ru, Sm and In are contained in the first component having a high resistance as 0.2 to 40 mol% as the second component. By containing it and forming a conductive path, electrons can be efficiently injected from the electron injection electrode into the organic light emitting layer. This is thought to be due to the inclusion of the second component in the first component, so that the conductive material exists in an island shape in the insulating material, and a hopping path for electron injection is formed. .
[0121]
By containing 0.2 to 40 mol% of the second component in the first component, it becomes possible to further suppress the movement of holes from the organic light emitting layer to the electron injection electrode, and the organic light emitting layer Can recombine holes and electrons efficiently.
The
[0122]
When providing a high-resistance inorganic electron injecting and transporting layer, it is equivalent to or more than conventional organic electron injecting and transporting layers and organic EL devices having organic electron injecting and organic electron transporting layers. In addition, it has high heat resistance and weather resistance, so it has a long life and good connectivity with the electron injection electrode, which is an inorganic material, so that there are few leaks and dark spots. There are advantages. Furthermore, unlike organic materials that are relatively expensive, inorganic materials for forming inorganic electron injecting and transporting layers are inexpensive, easily available, and easy to form inorganic electron injecting and transporting layers. The manufacturing cost of the element or the organic EL display panel can be reduced.
[0123]
The resistivity of the high resistance inorganic electron injecting and transporting layer is 1 × 10^-2Ω · cm〜1 × 10^-8It is preferably Ω · cm. By setting the resistivity of the inorganic electron injecting and transporting layer within such a range, it is possible to dramatically improve the electron injecting efficiency while maintaining high hole blocking property.
[0124]
The oxide of the first component usually has a stoichiometric composition, but may be slightly deviated from this to have a non-stoichiometric composition. The same applies to the oxide of the second component.
[0125]
The high-resistance inorganic electron injecting and transporting layer may further contain H as an impurity, Ne, Ar, Kr, Xe or the like used as a sputtering gas in total of 5 at% or less.
[0126]
The high and low resistance inorganic electron injecting and transporting layer is usually in an amorphous state.
[0127]
The high-resistance inorganic electron injecting and transporting layer preferably has a thickness of 0.2 to 30 nm, and particularly preferably has a thickness of 0.2 to 20. Even if the film thickness of the high-resistance inorganic electron injecting and transporting layer is less than 0.2 nm or more than 30 nm, the electron injecting function is not sufficiently exhibited.
[0128]
The high-resistance inorganic electron injecting and transporting layer can be formed by various physical or chemical thin film forming methods such as sputtering and vapor deposition, but is preferably formed by the sputtering method. In particular, it is preferable to form the inorganic electron injecting and transporting layer by a multi-component spackling method in which the first component and the second component are separately spucked as targets. According to the multi-source sputtering method, sputtering can be performed under conditions suitable for each target. Moreover, an inorganic electron injecting and transporting layer can also be formed by a one-way sparkling method using a mixed target of the first component and the second component.
[0129]
When the inorganic electron injecting and transporting layer is formed by the spackling method, the sputtering gas pressure is preferably set in the range of 0.1 to 1 Pascal. As the sputtering gas, an inert gas usually used in the sputtering method, for example, Ar, Ne, Xe, Kr, or the like can be used, and a nitrogen gas can also be used as necessary. At the time of sputtering, in addition to these sputtering gases, 1 to 99% oxygen gas may be mixed.
[0130]
As the sputtering method, a high-frequency sputtering method using an RF power source or a DC sputtering method can be used, and the power of the high-frequency sputtering using the RF power source is preferably in the range of 0.1 to 10 W / square centimeter, and the film formation rate. Is preferably in the range of 0.5 to 10 nm / min, particularly 1 to 5 nm.
[0131]
The substrate temperature during film formation is about 25 to 150 ° C.
[0132]
In the present invention, examples of the substrate for forming the organic EL structure include amorphous substrates such as glass and quartz, crystal substrates such as Si, GaAs, ZnSe, ZnS, GaP, and InP, and these crystal substrates. A substrate on which a crystalline, amorphous or metal buffer layer is formed can also be used. As the metal substrate, Mo, Al, Pt, Ir, Au, Pd, or the like can be used. Further, a resin material such as plastic or a flexible material can be used. The substrate material is preferably a glass substrate or a resin material. When the substrate is on the light extraction side, the substrate preferably has the same light transmittance as that of the electrode.
[0133]
As the glass material, alkali glass is preferable from the viewpoint of cost, but glass materials such as soda lime glass, lead alkali glass, borosilicate glass, aluminosilicate glass, and silica glass are also preferable. In particular, a glass material that is soda glass and has no surface treatment can be used at low cost.
[0134]
Further, in order to prevent oxidation of the organic layer and the electrode of the element, it is preferable to seal the element with a sealing plate or the like. In order to prevent moisture from entering, the sealing plate uses an adhesive resin layer to adhere and seal the sealing plate. Sealing gas is Ar, He, N₂An inert gas such as is preferable. The moisture content of the sealing gas is preferably 100 ppm or less, more preferably 10 ppm or less, and particularly preferably 1 ppm or less. There is no particular lower limit to the moisture content, but it is usually about 0.1 ppm.
[0135]
As the material of the sealing plate, a material different from that of the substrate can be used, but preferably the same as the substrate material or the one having the same thermal expansion coefficient and mechanical strength.
[0136]
The sealing plate may be held at a desired height by adjusting the height using a spacer. Examples of the material for the spacer include resin beads, silica beads, glass beads, glass fibers, and the like, and glass beads are particularly preferable. In addition, when a recessed part is formed in the sealing plate, the spacer may or may not be used.
[0137]
The spacer may be mixed in the sealing adhesive in advance or may be mixed during bonding. The content of the spacer in the sealing adhesive is preferably 0.01 to 30 wt%, more preferably 0.1 to 5 wt%.
[0138]
The adhesive is not particularly limited as long as stable adhesive strength can be maintained and airtightness is good, but it is preferable to use a cationic curing type ultraviolet curing epoxy resin adhesive.
[0139]
The emission color may be controlled by using a color filter film, a color conversion film containing a fluorescent substance, or a dielectric reflection film on the substrate.
[0140]
For the color filter film, a color filter used in a liquid crystal display or the like may be used. However, by adjusting the characteristics of the color filter according to the light emitted from the organic EL element and optimizing the extraction efficiency and color purity, Good.
[0141]
In addition, if a color filter that can cut off short-wavelength external light that is absorbed by the EL element material or the fluorescence conversion layer is used, the light resistance and display contrast of the element can be improved.
[0142]
Further, an optical thin film such as a dielectric multilayer film may be used instead of the color filter.
[0143]
The fluorescence conversion filter film absorbs EL emission light and emits light from the phosphor in the fluorescence conversion film, thereby converting the color of the emitted light. The composition includes a binder, a fluorescent material, It is formed from three light absorbing materials.
[0144]
Basically, a fluorescent material having a high fluorescence quantum yield may be used, and it is desirable that the fluorescent material has strong absorption in the EL emission wavelength region. In fact, laser dyes are suitable, such as rhodamine compounds, perylene compounds, cyanine compounds, phthalocyanine compounds (including subphthalocyanines) naphthalimide compounds, condensed ring hydrocarbon compounds, condensed heterocyclic compounds -A styryl compound, a coumarin compound, etc. may be used.
[0145]
As the binder, a material that basically does not quench fluorescence may be selected, and a binder that can be finely patterned by photolithography, printing, or the like is preferable. Further, when formed on the substrate in contact with the hole injection electrode, a material that is not damaged when the hole injection electrode (ITO, IZO, etc.) is formed is preferable.
[0146]
The light absorbing material is used when light absorption of the fluorescent material is insufficient, but may not be used when unnecessary. As the light absorbing material, a material that does not quench the fluorescence of the fluorescent material may be selected.
[0147]
As shown in FIG. 1, the organic EL device of the present invention includes, for example, substrate 1 / hole injection electrode 2 / metal layer 3 / insulating layer or resistance layer 4 / hole injection transport layer 5a, light emitting layer 5b, electron injection transport. The organic layer / inorganic electron injection / transport layer 6 / electron injection electrode 7 including the layer 5c are sequentially stacked. Moreover, it is good also as a reverse lamination in which the electron injection electrode 7 is formed in the board | substrate 1 side. The laminated structure may be an optimum laminated structure depending on required performance and specifications. The organic layer may have a multi-layer structure in which a hole injecting and transporting layer, a light emitting layer, an electron injecting and transporting layer, etc. are laminated, or a single layer structure in which the light emitting layer has an electron injecting and transporting function and a hole transporting function. It is good.
[0148]
The organic EL element is DC-driven or pulse-driven, and can be AC-driven. The applied voltage is usually about 2 to 30V.
[0149]
【Example】
  [referenceExample 1]
  BookreferenceAs shown in FIG. 2, the organic EL element described in the example has, on a glass substrate 1, a transparent conductive film ITO as a hole injection electrode 2: 100 nm and Pt as a hole injection metal layer 3: 0.5 nm. GeO₂ : In₂O_Three (Sputter target composition, 85:15 mol%) Inorganic hole injection layer 4 composed of 1 nm and the following chemical formula 15Similarly to the distyrylarylene derivative represented by16An organic light-emitting layer 5 having a film thickness of 100 nm to which 3% by volume of a distyrylaryleneamine derivative represented by the formula is added, an inorganic electron injection layer 6 of lithium fluoride: 0.3 nm, and 2% by volume of silver are added to magnesium. The electron injection electrode 7 having a thickness of 200 nm is sequentially laminated.
[0150]
Embedded image

[0151]
Embedded image

[0152]
The manufacturing method of this organic EL element is demonstrated concretely.
[0153]
First, the glass substrate 1 on which the hole injection electrode 2 was formed was ultrasonically cleaned for 10 minutes and then rinsed with pure water. Thereafter, baking was performed in an oven at 110 ° C. for 8 hours or more. UV / O on this ITO substrate_Three After cleaning, it is introduced into a vacuum apparatus and the inside of the tank is 1 × 10^Four The pressure was reduced to Pa or lower.
[0154]
Next, as the hole injection metal layer 3, Pt was deposited by EB vapor deposition at a deposition rate of 0.01 nm / sec to 0.5 nm. The conditions at this time were a voltage of 4.6 keV and a current value of 200 mA.
[0155]
While maintaining the reduced pressure state, the target is GeO₂ : In₂0_Three (85:15 mol%) was used to form an inorganic high resistance layer with a thickness of 1 nm and a hole injection layer with a total thickness of 1.5 nm. The condition at this time is 10% O in the sputtering gas.₂/ Ar, pressure: 0.15 Pa, input power: 0.8 W / cm² The film formation rate was 0.05 nm / sec.
[0156]
Further, while maintaining the reduced pressure, 3% by volume of the compound of Chemical Formula 16 was added to the compound of Chemical Formula 15 above, and the organic light emitting layer 5 was formed to a thickness of 100 nm by a resistance heating method at a deposition rate of 0.1 nm / sec. Vapor deposited.
[0157]
Subsequently, the electron injection layer 6 was vapor-deposited to a thickness of 0.3 nm using lithium fluoride by a resistance heating method at a vapor deposition rate of 0.01 nm / sec.
[0158]
Further, 2% by volume of silver was added to magnesium, and the electron injection electrode 7 was steamed to a thickness of 200 nm at a deposition rate of 0.1 nm / sec.
The organic EL element was produced as described above.
[0159]
  [referenceExample 2)
  Except that the inorganic high resistance layer was 3 nm and the Pt layer 0.5 nm was combined with a 3.5 nm hole injection layer.referenceThe structure was the same as in Example 1.
[0160]
  [referenceExample 3)
  The organic light emitting layer 4 is composed of tris (8-quinolinol) aluminum (hereinafter abbreviated as Alq3) with a film thickness of 100 nm.referenceThe structure was the same as in Example 2.
[0161]
  〔Example1]
  As shown in FIG. 3, as the organic hole injection layer 5a, N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine (TPD and (Omitted) except that a film thickness of 20 nm is inserted between the inorganic hole injection layer 4 and the organic light emitting layer 5b.referenceThe structure was the same as in Example 3.
[0162]
  [referenceExample4]
  The inorganic insulating layer is made of SiO.₂ : 3 nm, Pt layer: Example other than 0.5 nm hole injection layer combined with 0.5 nm1The structure is the same as that.
[0163]
  [Comparative Example 1]
  Inorganic hole injection layer is made of inorganic high resistance layer GeO₂ : In₂0_Three 1 nm only, except that no Pt metal layer is providedreferenceThe structure was the same as in Example 1.
[0164]
  [Comparative Example 2]
  Inorganic hole injection layer is made of inorganic high resistance layer GeO₂ : In₂0_Three : 3 nm only, except that no Pt metal layer is providedreferenceThe structure was the same as in Example 2.
[0165]
  [Comparative Example 3]
  Inorganic hole injection layer is made of inorganic high resistance layer GeO₂ : In₂0_Three : 3 nm only, except that no Pt metal layer is providedreferenceThe structure was the same as in Example 3.
[0166]
  [Comparative Example 4]
  Inorganic hole injection layer is made of inorganic high resistance layer GeO₂ : In₂0_Three : Example only except that 3 nm is provided and no Pt metal layer is provided.1The structure is the same as that.
[0167]
  [Comparative Example 5]
  Inorganic insulating layer SiO₂ : 3 nm only, except that no Pt metal layer is providedreferenceExample4The structure is the same as that.
[0168]
  [Comparative Example 6]
  As the inorganic hole injection layer, Mg is deposited to a thickness of 0.5 nm instead of Pt, and then the inorganic high resistance layer GeO₂ : In₂0_Three Except that the film thickness is 3nm and the total thickness is 3.5nm.referenceThe structure was the same as in Example 2.
[0169]
  [Comparative Example 7]
  GeO on ITO₂ : In₂0_Three Except for forming the hole injection layer first and then forming the Pt layer.referenceA device was produced in the same manner as in Example 1.
[0170]
In this element, when the organic layer was formed on the metal layer, the organic layer was repelled, and the organic thin film could not be formed uniformly.
[0171]
  the abovereferenceExample 14. Example 1A predetermined voltage was applied to each organic EL element of Comparative Examples 1 to 7 with the ITO electrode side being positive and the electron injection electrode side being negative, and a current density of 10 mA / cm² Voltage and brightness 100cd / m² The voltage was measured when
[0172]
The results are shown in Table 1 below.
[0173]
[Table 1]

[0174]
  Also onRealExamplesReference examplesThe measured values of the resistivity of the insulating layer and the high resistance layer used in 1 are shown below. In the measurement, the sample masked so as to have a predetermined area was sandwiched between the ITO transparent electrode and the Al electrode, and obtained from the applied voltage and current. Note that the measured value is likely to be affected by environmental humidity and noise level, and is considered to include an error.
[0175]
[Table 2]

[0176]
  From the above results,Reference examples 1-4Comparative Examples 1-5 and Examples1For eachRuSample, for examplereferenceExample 1 (driving voltage 6.6V, 10mA / cm² And Comparative Example 1 (driving voltage 12.6V, 10mA / cm² When the sample of the present invention is compared, the decrease in driving voltage is remarkable. In Comparative Example 3, the luminance is 100 cd / m.² When the voltage at the time of measurement was used for measurement, the device was destroyed before measurement.
[0177]
On the other hand, even if magnesium (work function 3.6 eV) whose work function is lower than that of ITO (work function 4.6 eV) is inserted instead of Pt (work function 5.4 eV), the driving voltage is obtained from the result of Comparative Example 6. There was no decline in
[0178]
In Comparative Example 7, no luminance was obtained, and the luminance was 100 cd / m.² The voltage drive voltage when This is probably because the leak voltage burned out first, and the drive voltage then increased abnormally. In addition, the luminance unevenness in the light emitting part was severe, and bright spots were observed.
[0179]
From the above results, it became clear that the drive voltage is lowered by inserting a metal having a higher work function than the hole injection electrode.
[0180]
  [referenceExample5]
  referenceFor the elements of Example 1 and Comparative Example 1, the current density was 100 mA / cm in an argon atmosphere.² The organic EL element was measured for the lifetime by continuously emitting light at a constant current of. The results are shown in FIG.
[0181]
  From the above results,referenceIt was found that the progress of the emission luminance reduction of the organic EL element in Example 1 was much slower than that of Comparative Example 1. This is considered to be due to leakage suppression due to the insertion of the high resistance layer and a decrease in the amount of heat generated due to a decrease in drive voltage due to the insertion of the metal layer.
[0182]
As described above, according to the present invention, by using a metal layer having a high work function and an insulating layer or a high-resistance layer as the inorganic hole injection layer, leakage is suppressed, and in addition, the insulating layer and the organic layer are By reducing the energy barrier, the driving voltage of the element can be lowered and the life of the element can be extended. Therefore, the present invention can be applied to various display devices of organic EL elements, and the effect is great.
[0183]
【The invention's effect】
As described above, according to the present invention, there is element reliability such as element leakage suppression obtained when an insulating layer or a resistance layer is used as a hole injection layer, and further, the driving voltage that is a disadvantage is increased. It is possible to provide an organic EL element that can be prevented and has high reliability and low driving voltage.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a basic configuration of an organic EL element of the present invention.
[Figure 2]reference2 is a schematic cross-sectional view showing a basic configuration of an organic EL element of Example 1. FIG.
FIG. 3 Example1It is a schematic sectional drawing which shows the basic composition of this organic EL element.
[Fig. 4]referenceExample5It is the graph which showed the measurement result of the lifetime characteristic.
[Explanation of symbols]
1 Substrate
2 Hole injection electrode
3 Metal layers
4 Insulation layer / resistance layer
5 Organic layer
5a Hole injection transport layer
5b Light emitting layer
5c Electron injection transport layer
6 Inorganic electron injection layer
7 Electron injection electrode

Claims (5)

Between a pair of electrodes composed of a hole injection electrode and an electron injection electrode, a metal layer containing a metal element having a work function larger than that of the hole injection electrode from the hole injection electrode side to the electron injection electrode, an inorganic positive electrode It has an organic layer including a hole injection layer and a light emitting layer in this order,
The organic layer including the light emitting layer has a hole injection transport layer made of an organic compound between the inorganic hole injection layer and the light emitting layer,
The organic EL element, wherein the inorganic hole injection layer is a layer made of GeO ₂ and In ₂ O ₃ formed on the metal layer by a sputtering method.   2. The organic EL device according to claim 1, wherein the metal layer contains one or more elements selected from Pt, Au, Pd, Ni, Re, Co, Se, and Ir.   The organic EL element according to claim 1, wherein the metal layer has a thickness of 0.1 to 2 nm. The metal layer is made of platinum and has a thickness of about 0.5 nm, and the inorganic hole injection layer made of GeO ₂ and In ₂ O ₃ has a thickness of 1 to ₃ nm. The organic EL device according to claim 3.   5. The organic EL element according to claim 1, wherein the hole injection electrode, the metal layer, and the insulating layer or the resistance layer have a light transmittance of 80% or more.

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